Corrugated flexible plastic sheets are widely used in buildings for roofing or otherwise covering portions of the building to protect from ambient effects, such as sun radiation, rain, dust, etc. In some cases, illumination of the interior part of the building by natural light is required, e.g. greenhouses or industrial facilities roof or walls which require natural lighting during daylight times. In such cases, the corrugated sheets may have certain levels of transparency, as may be desired.
The main benefits of assembling transparent corrugated plastic sheets is illumination energy saving. To further reduce the energy costs of such buildings, the connection between each transparent corrugated plastic sheets and its neighboring sheets (either transparent or not) should be sealed to prevent various environmental effects, for example, penetration of rain into the building which is covered by the corrugated sheets, heat leakage due to temperature differences, penetration of wind and/or dust, and the like. The corrugation of the plastic sheets provides the sheets with the necessary strength while maintaining the sheets' flexibility in both directions of the sheet—parallel to the corrugation waves (which is easier to accomplish) and perpendicular to that direction.
Typically, roofing (or otherwise covering a large area) with corrugated sheets involves a certain overlap of one sheet over or under its neighboring sheet. Since sheets with identical corrugation profile are used for covering a certain area, typically a peak of a corrugation wave at the very end of that sheet is used to overlap (or under lap) a similar wave peak of the neighboring sheet. FIG. 1A is an isometric view and FIG. 1B is a side view of an elongated assembly of bottom profile 12B that fits the concaved side 13 of the bottom sheet 10A so as to touch it along the peak 13A of the corrugation wave of corrugated sheet 10A. Bottom profile 12B provides counter-base for threading connecting bolts/screws 14 that are inserted from above through a top elongated fixing element 12A, through top sheet 10B and through bottom sheet 10A, and are then threaded into the bottom elongated element 12B thus clamping corrugated sheets 10A and 10B to each—other along overlapping peaks of waves of the corrugations.
Such connecting elongated elements are typically designed for particular installations having a particular length that corresponds to the particular lengths of the corrugated sheets used in the installation. Such way of connecting elongated elements is relatively expensive and do not provide flexibility of use when it is required to cover an area using corrugated sheets of length different than the standard length because there is a need to match the length of the connecting elements to that of the corrugated sheets. This increases the overall cost of the building both in materials and in installation time. Furthermore, at least two workers are needed in order to assemble the connecting elongated elements, one on each side of the corrugated sheet. This solution involves complex installation and requires specific adaptation of elements in cases where the length of the sheets is different than the common length. Additionally, adapting this solution for installations where the covered plane is not flat, but rather concaved or convex with the curved line residing in a plane perpendicular to the plane of the roof and parallel to the corrugated peak line, requires on-site adaptation of the elongated elements to that curvature.
As seen in FIG. 1C, another solution known in the art for fastening corrugated sheets to each other is self-grip lap fastener, which is a flat thin metal piece in which a tread is pre-prepared, having several claws which are made to punch into the external (usually bottom) side of one of the corrugated overlapping sheets and accept a screw that is inserted through the top sheet and the bottom sheet and screwed into its thread. This solution suffers of a main disadvantage—when installed, the self-grip fastener punches through the sheet to which it is attached, thus creating cracks that later expend and lead to leakage problems.
FIGS. 1D and 1E depict another solution known in the art for fastening corrugated sheets to each other using rubber stitching fastener with internal threading. When in loose position it has a cylindrical main body that may be inserted through overlapping through-holes in the overlapping top and bottom corrugated sheets and then by screwing the bolt the rubber element (or EPDM element) is pressed and expends its diameter so as to tighten the sheets to each other. This solution is relatively expensive and involves installation complexity.